In a rotary machine such as a centrifugal compressor, gas is compressed by a centrifugal force which is generated when the gas passes through in a radial direction of a rotating impeller. As the centrifugal compressor, an uniaxial multistage centrifugal compressor having a structure in which an impeller compressing gas is attached on a single shaft, and a centrifugal compressor with a built-in speed-increasing gear (hereinafter, referred to as a geared compressor) having a structure in which impellers are attached on shaft ends of a plurality of pinion shafts are known. As the geared compressor, a type is known, in which a fluid is compressed by a plurality of compression portions having the impellers provided on the shaft ends of the plurality of pinion shafts.
As the geared compressor, for example, PTL 1 discloses a double flow geared compressor in which compression portions having the same configuration are provided on both ends of each of driven shafts which are pinion shafts to which rotation of a driving shaft is transmitted. In this geared compressor, two compression portions are rotated by one driven shaft, gas is simultaneously compressed from both sides, and the two compression portions are operated like one compression portion. Accordingly, an increase in the capacity of the entire geared compressor is realized without increasing the diameter of the impeller.